This is one possibility I proposed to RMS. Essentially, I proposed that
all Invariant Sections had to be placed in debian/copyright, and that
any duplicates of his Invariant text in the "actual" documentation would
be modifiable.
That is unacceptable because it would allow modified versions of the
GNU Manifesto. The GFDL, like the previous Emacs Manual license, was
designed to require every copy of the Emacs Manual to include an
unmodified copy of the GNU Manifesto.
I hope that Debian, if it adopts a version of your guidelines, will
modify them so as to accept the Emacs Manual.